I thought it would be useful to start a topic regarding different airspeeds in aviation since some folks seem confused by the airspeed limitations found in Infinite Flight. The 4 types are airspeed are easily remembered with the acronym ‘ICE T’:
- I - Indicated airspeed (IAS) - the airspeed displayed on the airspeed indicator, as measured by air entering the pitot tube. This is the speed pilots use to fly by, including takeoff and landing speeds. This is also the speed ATC wants the pilot to fly when they give a speed restriction. There is an upper indicated airspeed limitation which a pilot must never exceed, and it varies from aircraft to aircraft, and sometimes varies according to altitude for a particular aircraft.
- C - Calibrated airspeed - not applicable in IF, it is airspeed corrected for instrument error.
- E - Equivalent airspeed - also not applicable in IF, airspeed corrected for the compressibility effects of air at higher airspeeds.
- T - True airspeed - the actual speed of an aircraft moving through the air. For example, at sea level, an indicated airspeed of 290 kts will yield a true airspeed very close to 290 kts. As the aircraft climbs and the air becomes less dense, the aircraft needs to move faster through the air to get the same amount of air moving through the pitot tube to indicate 290 kts. At 30,000 ft (standard day temp/pressure) 290 kts indicated will be approximately 474 kts TAS!
Additionally, moving beyond ICE T, the Mach number is the ratio of the aircraft’s speed to the speed of sound. Most civilian jet aircraft cruise between Mach .75 and .85. In the example of 290 KIAS at 30,000 ft, the Mach number would be approximately .80
Lastly, the ground speed is the speed that determines how long it takes to get from A to B. With zero wind, true airspeed=ground speed. But winds aloft can have a big effect on ground speed. In our example, with a direct 100 kt headwind, the ground speed is 374 kts, with 290 KIAS and 474 KTAS. With a 100 kt tailwind, ground speed is 574 kts, with 290 KIAS and 474 KTAS.
Bottom line: Don’t complain about the airspeed limitations in IF. It adds realism to the sim. No airliner is (currently) flying around with an indicated airspeed of 500 kts.